Mid-IR imaging of the transitional disk of HD169142: Measuring the size of the gap

TL;DR

This study uses mid-infrared imaging and radiative transfer modeling to measure the size of a large gap in the disk of HD169142, revealing a complex disk structure with an inner wall at about 23 AU and additional hot dust close to the star.

Contribution

It provides the first direct measurement of the gap size in HD169142's disk using MIR imaging and models the disk's structure, suggesting such gaps may be common in group I Herbig Ae/Be disks.

Findings

The outer disk wall is located at approximately 23 AU.

An additional hot dust component exists close to the star.

A hydrostatic inner disk alone cannot explain the observed NIR flux.

Abstract

The disk around the Herbig Ae star HD\,169142 was imaged and resolved at 18.8 and 24.5\,$\mu$m using Subaru/COMICS. We interpret the observations using a 2D radiative transfer model and find evidence for the presence of a large gap. The MIR images trace dust that emits at the onset of the strong rise in the spectral energy distribution (SED) at 20\,$\mu$m, therefore are very sensitive to the location and characteristics of the inner wall of the outer disk and its dust. We determine the location of the wall to be 23$^{+3}_{-5}$\,AU from the star. An extra component of hot dust must exist close to the star. We find that a hydrostatic optically thick inner disk does not produce enough flux in the NIR and an optically thin geometrically thick component is our solution to fit the SED. Considering the recent findings of gaps and holes in a number of Herbig Ae/Be group I disks, we suggest that such disk structures may be common in group I sources. Classification as group I should be considered a support for classification as a transitional disk, though improved imaging surveys are needed to support this speculation.